RFR: 8291067: macOS should use O_CLOEXEC instead of FD_CLOEXEC [v4]

[Gerard Ziemski]

> O_CLOEXEC is also available on macOS (__DARWIN_C_LEVEL >= 200809L), so use it same as on linux.

Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:

  create our own test file, to guarantee it will exist

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9663/files
  - new: https://git.openjdk.org/jdk/pull/9663/files/b3cb4f29..42532c2c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9663&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9663&range=02-03

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9663.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9663/head:pull/9663

PR: https://git.openjdk.org/jdk/pull/9663